Working memory (WM) is a system for maintaining online representations of information in the service of virtually all explicit cognitive processes (e.g., memory retrieval, problem solving). WM's core role in cognition is also highlighted by strong correlations between WM capacity and fluid intelligence as various measures of scholastic achievement. Furthermore, deficits in WM performance are associated with prevalent clinical disorders, including attention deficit/ hyperactivity disorder (ADHD) and schizophrenia. The proposed research in the parent grant to this supplemental application will address fundamental questions regarding the basic determinants of capacity limits in WM. Is capacity limited by a maximum number of items that can be represented simultaneously in WM? Or is it limited by the available mnemonic resolution (i.e., clarity) necessary for representing a given set of items? Our preliminary data suggest that rather than being determined by a single factor, number and resolution are distinct facets of WM capacity. The proposed research seeks to further detail how these two factors interact to limit WM performance by means of a combination of psychophysical procedures, human electrophysiological recordings (ERPs), and novel neural decoding techniques using FMRI. This supplemental application expands the scope of the parent project by means of a large- scale individual differences study that examines the nature of the relationship between WM capacity and standard measures of fluid intelligence (e.g., Stanford Binet IQ). Given that the link between WM capacity and fluid intelligence is a core motivating factor for WM research, high value is placed on research that can elucidate why these links are present in the first place. Our preliminary findings indicate that while the number of representations that can be held in WM strongly predicts fluid intelligence, the precision or resolution of those memories showed no correlation with intelligence. We will replicate and extend this result using a broader range of behavioral and neural measures of memory and intellectual ability, with the goal of better understanding how intelligent behavior is supported by lower level memory processes. This project will inform both cognitive models of how WM is organized across stimulus modalities, and the precise aspects of WM function that influence individual variations in fluid intelligence. A better understanding of these basic research questions will enable a more precise characterization of psychopathologies that involve impaired cognitive processing, supporting both basic and translational research in the domain of mental health. PUBLIC HEALTH RELEVANCE: This proposal outlines a supplemental project that expands the scope of a parent grant project whose broad aims are to better characterize the nature of capacity limits in human working memory. This memory system is a core part of most cognitive processes, and capacity in this system is correlated with fluid intelligence and scholastic achievement. The supplemental proposal focuses on the relationship between working memory and fluid intelligence, following up on preliminary findings that while the number of items a person can maintain in working memory strongly predicts fluid intelligence, no such relationship was observed between the precision of the stored memories and intelligence. Given that the relationship between working memory and broad measures of intellectual ability constitute a core motivation for research in this area, a better understanding of how basic memory processes support intelligent behavior is highly desirable. The proposed research accomplishes this goal by characterizing why the number of items that can be stored in working memory relates to fluid intelligence, and providing further evidence on the broad taxonomy of visual working memory.